Bridge Maintenance Alternatives and Associated Cost

The bridge maintenance alternatives presented in this paper include both preventive and essential maintenances with actual cost data, as well as “do nothing”. The effects of the five different maintenance alternatives, namely, “minor concrete repair”, “silane treatment”, “cathodic protection”, “rebuild” and “do nothing” on individual bridge condition and safety indices over time have been studied as shown in Tables 1 and 2 (Denton, 2002). For example, the “minor concrete repair” results in a decrease of bridge condition index (CI) between 2 and 3 with a triangular probability distribution. The mode of the triangular probability distribution is 2.5, indicating that the most likely decrease of the bridge condition index is 2.5 (see Table 1). Meanwhile, the “minor concrete repair” causes a delay in deterioration of bridge safety index (SI) when the bridge condition index is less than 1.0, in other words, there is no deterioration of the bridge safety index after the “minor concrete repair” maintenance action is applied, and the deterioration of the bridge safety index resumes after the bridge

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M. Pandey et al. (eds), Advances in Engineering Structures, Mechanics & Construction, 833-840.

© 2006 Springer. Printed in the Netherlands.

condition index reaches 1.0. The “silane treatment” affects only the deterioration rates during the maintenance effective duration that has a triangular probability distribution between 7.5 and 12.5 years. The bridge condition and safety indices will not change in the first 12.5 years after the “cathodic protection” maintenance action is applied. The “rebuild” is the only essential maintenance actions in this study. If this action is applied, the bridge condition index will be set to zero and the bridge safety index will be assigned to the safety index of the rebuilt bridge. Meanwhile, the deterioration of the bridge condition index will start between 10 and 30 years after “rebuild” with a triangular probability distribution mode of 15 years. The deterioration of the bridge safety index will begin when the bridge condition index reaches 1.0. Table 3 presents the associated cost of the five alternatives considered. Figures 1 to 4 shows the effects of the preventive (“minor concrete repair”, “silane treatment” and “cathodic protection”) and essential (“rebuild”) maintenance alternatives on the mean values of bridge condition and safety indices over time.

Table 1: Effect of Bridge Maintenance Alternatives on Mean Condition Index (after Denton, 2002)

Bridge

Maintenance

Alternatives

Decrease in Condition Index

Delay in Deterioration (years)

Reduced

Deterioration

Rate (year-1)

Maintenance Effective Duration (years)

Minor Concrete Repair

T(2.0, 2.5, 3.0)

Silane Treatment

T(0.00, 0.01,0.03)

T(7.5, 10.0, 12.5)

Cathodic Protection

12.5

Rebuild

set to zero

T(10, 15, 30)

Do Nothing

Note: T (minimum value, mode, maximum value) represents the triangular probability distribution.

Table 2: Effect of Bridge Maintenance Alternatives on Mean Safety Index (after Denton, 2002)

Bridge

Maintenance

Alternatives

Increase in Safety Index

Delay in Deterioration (years)

Reduced Deterioration Rate (year-1)

Maintenance Effective Duration (years)

Minor Concrete Repair

CI<1.0

Silane Treatment

T(0, 0.007, 0.018)

T(7.5, 10.0, 12.5)

Cathodic Protection

12.5

Rebuild

set to SI

CI<1.0

Do Nothing

Note: T (minimum value, mode, maximum value) represents the triangular probability distribution.

Table 3: Cost for Bridge Maintenance Alternatives (after Denton, 2002)

Bridge Maintenance Alternatives

Cost

Minor Concrete Repair Silane Treatment Cathodic Protection Rebuild Do Nothing

T(16, 3605, 14437) T(0.3, 39,77)

T(19, 2604, 5189) T(247, 7410, 28898) 0.0

Note: T (minimum value, mode, maximum value) represents the triangular probability distribution.